The use of various finishing processes is well-known in the manufacture of textile and nonwoven materials for imparting stain repellence, antistatic properties, ultraviolet fade resistance, fabric softening, and anti-microbial behavior, as examples. Finishing processes are most commonly applied by passing the fabric or nonwoven material through a chemical bath, in which the fabric picks-up, or absorbs, some of the chemical bath, followed by a thermal curing operation. Typically, finishing processes are applied to woven or knitted fabric, or non-woven substrates after they have been bleached and strengthened (such as through a mercerization process) and dyed. U.S. Pat. No. 6,525,127 describes the use of various fluorochemicals in a dip tank for finishing treatments for fabrics. In addition to dipping the fabric into a bath, conventional alternative methods involve the use of sprays, foams, roll-on addition of liquid chemicals, or atomizers. Silicones, siloxanes, fatty acids, and esters may also be added to the dip tank for fabric softening applications, as well as a means to impart stain repellency. To assist in the solubility of compositions which are not normally soluble in water, surfactants and emulsifiers are often added to obtain a consistent and uniform suspension of chemicals in the finishing bath.
Wet processes have several disadvantages. For example, (1) drying and curing may take several minutes, and may expose the material to high temperatures; (2) large ovens and frames are required for preventing shrinkage of the wet fabric; (3) additives necessary for solubilizing the desired compositions may penetrate the substrate or generate a thin film thereon, and may either decompose, leaving break-down products, or remain on the fabric as impurities during drying and curing; (4) some of these additives may assist in the removal of the finishing compositions when the fabric is dry cleaned, because of the non-polar nature of the dry cleaning process; (5) the chemical composition of the finishing bath may change over time because of different rates of absorption of the chemical species, with the result that finishing bath chemicals must be periodically replaced, thereby generating both cost and environmental impact; and (6) openings which naturally occur in woven or knitted yarns and provide comfort and breathability may clog as a result of the accumulation of macoscopic amounts of chemicals, as well as increasing the cost of finishing.
Many fabrics, such as leather, silk, rayon and wool, are best cleaned using non-water-based dry-cleaning processes. Other fibers, such as polypropylene and nylon used in nonwovens and textiles, are damaged by the heat required to dry and cure the active chemicals applied by a conventional wet finishing process. Polyester becomes “stiffer” due exposure to high-temperatures during curing.
Dry process methods used to achieve similar finishing properties while avoiding these difficulties include vacuum-based plasmas and atmospheric pressure plasmas, and have been used to apply finishing materials to flexible substrates, such as textiles and nonwoven materials. Plasma polymerization is an inherently low-temperature process, effectively eliminating the drying and curing steps required for wet finishing. This enables treatment of heat-sensitive fabric, saves energy, and reduces the cost and complexity of process equipment, because no tenter frames or ovens are required. Vacuum-based plasmas are generally easier to generate than atmospheric-pressure plasmas because the loss rate and generation rate of electrons are more readily controlled, and may operate with many applied feed gases. Atmospheric pressure plasmas are prone to arcing once a certain power density is exceeded inside the plasma volume, because of the greater density of electrons that result from the higher feed gas density.
Plasmas produce short-lived, active, chemical radicals, such as CFx from fluorochemical feed gases for textile finishing processes. Once generated in the gas phase by impact with energetic electrons with a fluorochemical feed gas, CFx radicals may attach to the surface of a fabric or other substrate, resulting in a low surface energy treatment that is hydrophobic to water and repellent to oils. This approach is described in U.S. Pat. No. 3,674,667 for “Process For Increasing Water Repellency Of Cotton Cloth” which issued to Jean P. Manion and Daniel J. Davies on Jul. 4, 1972.
The use of vacuum-based plasma for batch treatment of rolls of fabric or rolls of yarn is described in U.S. Pat. No. 4,479,369 for “Apparatus For Treating A Textile Product With The Use Of Low-Temperature Plasma” which issued to Yoshikazu Sando et al. on Oct. 30, 1984, and in U.S. Pat. No. 4,550,578 for “Apparatus For Low-Temperature Plasma Treatment Of A Textile Product” which issued to Yoshikazu Sando et al. on Nov. 5, 1985.
Alkylated fluorochemical oligomers have been successfully used in wet finishing processes, as described in U.S. Pat. No. 6,818,253 for “Method Of Producing Textile Substrates Having Improved Durable Water Repellency And Soil Release” which issued to William C. Kimbrell on Nov. 16, 2004, and U.S. Pat. No. 7,049,379 “Alkylated Fluorochemical Oligomers And Use Thereof In The Treatment Of Fibrous Substrates” which issued to Chetan P. Jariwal et al. on May 23, 2006, and show much improved durability of the finishing process against degradation after multiple laundry cycles.
Fluorochemical acrylates can also be polymerized using plasmas, and have been applied using both vacuum-based and atmospheric pressure plasmas. Such compositions are generally durable against multiple laundering processes. However, the long-chain fluorochemicals most effective for water and oil repellency are rapidly fragmented into CFx and COxHy moieties by impact from energetic plasma electrons, and the benefit from having an attached binding acrylate group may be lost. The fragmentation problem has been addressed by pulsing the plasmas; that is, by rapidly switching the electrical power applied to plasma on and off. The “on” period results in fragmentation of the feedgas followed by recombination, polymerization and cross-linking of the fluorochemical species, while during the “off” period, gas-phase collisional-recombination of the radical fragments reformulates a complex, fluorochemical polymer—hopefully having both the long-chain fluorinated group, used to repel water and oil, and the organic linking group suitable for binding to the textile—which may diffuse to the substrate without further fragmentation. By independently controlling the plasma “on” time and the plasma “off” time, the fragmentation rate and the gas-phase recombination rate may be controlled.
“Surface Coatings” by Jas Pal Singh Badyal et al., International Publication Number WO 98/58117, teaches a process whereby a stationary surface is exposed to a pulsed, vacuum-based plasma during passage of a perfluoralkyl acrylate feed gas, is coated by a film having both water and oil-repellent properties on the surface. A similar method was used in U.S. Patent Publication 2004/0152381, in which a pulsed plasma discharge was employed under vacuum conditions, with a fabric sample that was either static or slowly moving (0.4-0.6 m/min). The fluorocarbon feedstock is introduced in vapor form into a vacuum chamber, either using the equilibrium vapor pressure of the feedstock, or by directing a liquid feed into a heated tube, which converts the liquid into vapor. Fluorocarbon feedstocks include perfluorooctyl acrylate, which was also used in the WO 98/58117 patent, and perfluorododecene. Prior to treatment the fabric was dried to a chosen moisture level. U.S. Patent Publication 2004/0152381 also states that atmospheric pressure plasma excitation could be used, but does not teach how to perform the process at this pressure.
The electrodes for generating the plasma in U.S. Patent Publication 2004/0152381 are disposed in the vacuum chamber into which the fluorocarbon vapor is introduced, the plasma operating at the vapor pressure of the fluorocarbon gas. Similar results to those of the WO 98/58117 Publication were observed.
U.S. Patent Publication 2004/0152381 teaches that it is preferable to generate film coatings on the individual fibers having thicknesses between 2.5 nm and 20 nm in order to produce a fabric finish that has water and oil repellency with “excellent” durability against multiple agitation-laundry and dry-cleaning cycles, while also maintaining sufficient fabric air permeability for comfort. No laundry durability data is provided in the 2004/0152381 Publication.
Most plasmas do not penetrate sufficiently deeply into a film, so it is difficult to produce a film that is thicker than 20 nm. Layering methods where thin films are incrementally added are too slow for use in textile manufacturing.
U.S. Pat. No. 5,041,304 for “Surface Treatment Method” which issued to Yukihiro Kusano et al. teaches the use of an atmospheric pressure dielectric barrier discharge (DBD) in which the electrodes are covered with an insulator, or dielectric material, and a feedgas including a mixture of an inert gas (He) and a gas-phase, fluorinated compound, to deposit a water repellant film on a fabric.
In AATCC Review, 6, pages 21-26, April 2006) by Maria C. Thiry it is stated that: “the problem with conventional plasma processes is that surface molecular sophistication is severely limited by the aggressive nature of the plasma . . . . Essentially the plasma destroys any complex or long-chain molecule injected into the plasma as a precursor of the process.” Thus, it is presently believed that high-power plasmas generate greater electron densities in the plasma and higher electron energy distributions which favors the fragmentation of the feedgas, and results in more product scrambling. International Publication No. WO 98/58117 and U.S. Patent Application Publication No. 2004/0152381 teach the use of low average powers. As an example, U.S. Publication No. 2004/0152381 teaches time-averaged power densities in the range between 1.1×10−4 W/cm2 and 2.27×10−4 W/cm2. Such low power densities are used to obtain plasmas with a low density of electrons and ions, because the electrons have sufficient energy to decompose the complex, fluorochemical monomers. The '304 patent does not disclose plasma power levels, but DBDs typically operate at low power densities.
Accordingly, it is an object of the present invention to provide an apparatus and method for finishing fibrous woven and nonwoven materials while maintaining open spaces between neighboring yarns for woven materials.
Another object of the present invention is to provide an apparatus and method for finishing fibrous woven and nonwoven materials wherein the finished materials are durable against water-based laundry processes, dry-cleaning, and surface abrasion.
Still another object of the present invention is to provide an apparatus and method for finishing fibrous woven and nonwoven materials effective for heat sensitive fabrics.
Yet another object of the present invention is to provide an apparatus and method for finishing fibrous woven and nonwoven materials without the use of emulsifiers and surfactants.
It is yet another object of the present invention to provide a method for finishing fibrous knitted, woven and non-woven materials without requiring a thermal curing process.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.